The present invention generally relates to amplified stimulated emission (ASE) sources and methods for generating ASE and, in particular, to a source and method, which may be used with a fiber optic gyroscope, for generating ASE using a coupler mechanism to isolate pump light entering a doped element, such as a doped fiber, from ASE leaving the doped fiber.
Many sensors and communications devices require a ASE source with a stable centroid (or average) wavelength over time and over a broad temperature and drive current range to operate properly. In a typical broadband source, a wavelength division multiplexer (WDM) is employed to separate pump light, or laser light, from ASE generated by a length of erbium doped fiber (EDF). In particular, the WDM receives pump light from a pump source and transmits the pump light to the EDF. In response to the pump light, the EDF emits ASE back into the WDM. The WDM routes the ASE to a sensor, or for example a gyroscope. Unfortunately, WDMs are relatively costly which increases the cost of the laser light source. The WDM is also a major contributor to instability of the desired stable centroid wavelength.
Accordingly, there is a need in the art for an ASE source and method which provides ASE having a relatively stable centroid wavelength, which eliminates the need for a WDM and which uses a coupling mechanism to separate pump light and ASE.
This need is met by a source, system and method in accordance with the present invention in which a coupler mechanism, which may be a fiber coupler, transmits pump light from a pump source to a doped fiber, transmits ASE from the doped fiber and isolates the pump light and the ASE from one another.
In accordance with one aspect of the present invention, a source is provided in which a pump source generates pump, or laser, light. A doped fiber, such as an erbium doped optic fiber, generates ASE based on the pump light. A coupler mechanism interposed between the pump source and the doped fiber receives the pump light from the pump source, transmits the pump light to the doped fiber, transmits the ASE from the doped fiber and isolates the pump light and the ASE using phase conditions.
Although the coupler mechanism is generally shown as a two by two fused fiber coupler, any coupler may be advantageously employed in the present invention. Specifically, the coupler mechanism may comprise a fiber coupler including a first port for receiving the pump light, a second port for transmitting the pump light to the doped fiber and for receiving the ASE from the doped fiber, a third port for receiving the amplified stimulated emission from the doped fiber and for transmitting the pump light to the doped fiber and a fourth port for transmitting the amplified stimulated emission. A feedback reflector, such as a reflective Bragg grating, may reflect a portion of the amplified stimulated emission back into the doped fiber to substantially lock a wavelength of the amplified stimulated emission generated by the doped fiber. In addition, by reflecting the portion of the ASE back into the fourth port of the fiber coupler, almost all of the generated ASE will exit the fourth port due to the principle of reciprocity.
In accordance with another aspect of the present invention, a system is provided comprising a source and a sensor. The source generates ASE which is used by the sensor for sensing a parameter. The source comprises a pump source for generating pump light, a doped fiber for generating ASE based on the pump light, and a coupler mechanism. The coupler mechanism receives the pump light from the pump source, transmits the pump light to the doped fiber, transmits the ASE from the doped fiber and isolates the pump light and the ASE using phase conditions. A sensor senses a parameter, such as movement, using the ASE. The sensor may be a fiber optic gyroscope.
In accordance with yet another aspect of the present invention, a method for generating ASE is provided. The method comprising the steps of: generating a pump light; transmitting the pump light through a coupler mechanism to an doped fiber; generating ASE by the doped fiber based on the pump light; and transmitting the ASE through the coupler mechanism. The method may further comprise the step of reflecting a portion of the ASE back into doped fiber through the coupler mechanism with a Bragg grating.
These and other features and advantages of the present invention will become apparent from the following detailed description, the accompanying drawings and the appended claims.